Lasers are used in a wide variety of applications, and it is often necessary to ascertain the precise wavelength of the laser light being used, for a number of reasons. Accordingly, instruments known as wavelength meters have been developed for rendering precise measurements of the wavelength of laser light.
Among the wavelength meters in existence is the device disclosed in U.S. Pat. No. 4,173,442 to Snyder. The Snyder device includes a Fizeau interferometer into which laser light is directed, and the interferometer produces an interference fringe pattern which is received by a photo diode array. In accordance with the Snyder disclosure, the photo diode array generates an electrical signal representative of the fringe pattern, and the signal is sent to a computer. Then, the computer determines the wavelength of the laser light by analyzing the spatial period and phase of the fringe pattern. To simplify analysis, Snyder discloses a somewhat complicated optical system the components of which must be precisely positioned relative to each other, to produce a fringe pattern composed of straight co-parallel lines of equidistant spacing.
U.S. Pat. No. 5,168,324 to Hackel et al. discloses an improvement to the Snyder device. In accordance with Hackel et al., a wedge that has an elliptically-shaped face is interposed in the optical path of a Snyder-type device to improve the accuracy of the Snyder-type device. Like Snyder, however, Hackel et al. requires the use of a relatively complicated optical system having precisely positioned components.
Snyder and Hackel et al. are representative of many if not most wavelength meters currently in use, in that they require the use of a relatively complicated optical system having precisely positioned components. As the skilled artisan will appreciate, it can be time-consuming and therefore expensive to precisely position a number of components for each wavelength meter that is to be used.
Further, analytically accounting for temperature variations measurement-to-measurement has not heretofore been suggested in the prior art. Such variations can cause unwanted movement of the precisely positioned optical components. Snyder, like other prior art devices, deals with such variations not by analysis, but by requiring the use of a heating device to maintain the Snyder apparatus at a predetermined temperature. Unfortunately, it can be difficult at best to maintain the entire base plate on which the optical components rest, as well as the components themselves, at a constant temperature, due to temperature gradients which are inevitably introduced by the heating device.
As recognized by the present invention, a structurally simple wavelength meter can be provided which can generate very accurate wavelength measurements and analytically account for temperature variations affecting the optical path.
It accordingly is an object of the present invention to provide a simplified wavelength meter of a very compact size. A further object of the present invention is to provide a wavelength meter having a minimum of the optical elements while providing a wavelength measurement resolution of a few parts in 10.sup.7. Still another object of the present invention is to provide a wavelength meter which minimizes the influence of ambient temperature changes on the accuracy of the wavelength meter. A still further object of the present invention is to provide a wavelength meter which is relatively impervious to creep and leaps in the wavelength readout caused by temperature-induced mechanical stress on the wavelength meter components.